Material transfer vehicles and other machines used to transfer heavy materials often include mechanisms to move the material out of the machine and deliver the material in a desired location. Some may include mechanisms so simple as means to lift one end of a container to allow the material to slide via gravity out the lower end. However, many materials are not readily induced to slide across any surface by mere gravity, or at least not to move in a reasonable amount of time. Further, including on the vehicle a container that may be lifted by one end requires a mechanism with enough power to lift one end of the container; many materials are so dense that the power requisites to lift an end of the container are prohibitively expensive.
Other material transfer mechanisms may include augering means. Materials conducive to auguring typically include fungible small pieces and work best when auguring nearly level but may also be used to move materials upwards. Pneumatic and/or vacuum devices may also be used to move material yet, once again, materials best moved in that way are materials that act like fluid or have fluid-like properties such as grain, sand, and semi-liquids.
Yet other materials may be moved via an elevator mechanism. Some elevator mechanisms include moving platforms, perhaps accompanied by a plurality of shelves or, alternatively, a plurality of buckets. Other elevator mechanisms may include drag slat chains. Drag slat chains include parallel chains associated with each other via spaced apart slats. The slats act to support the material's movement toward the direction of travel as the chains move the slats. The chains are moved using sprockets, wheels, rollers, or other devices that temporarily engage the chain as it is turned around the sprocket or wheel and disengage when the direction of travel of that portion of the chain is reversed. This approach is often used with heavy, chunky material such as hot asphalt.
A problem with prior art means of moving heavy materials using drag slat chains in an elevator type of arrangement is that the chains are prone to wear. The wear is expedited when the chain moves a heavy load without adequate tension on the chain; further, wear occurs if the chains are not evenly tightened or a shock load occurs. The problem of maintaining proper chain tension has been a long-standing one and includes two aspects. The first aspect is the avoidance of too much tension which causes friction and requires excessive power to move the drag slat chain. The second aspect is the avoidance of too little tension which will result in sag which, when tightened, can cause the chain to “jump” resulting in being out of phase with the other chain. Out of phase chains often result in breaking one of the chains.
The chains on a drag slat device are expensive to replace and time consuming to repair. Prior means to address the issues presented by too much or too little tension included the use of hand-turned threaded bolts to adjust the tension on the chain a) by moving the sprocket (or wheel or roller or other driving means) around which the chain moved or b) by moving a structure upon which the sprocket (or wheel or roller) was mounted to achieve that effect. Where such means were employed, hand adjustment of one chain and then the other was likely to cause uneven and inexact tensioning and often those were the results. Alternatively, if such adjustment was done simultaneously, the machine would have to be deactivated for accurate adjustment. For example, the sprockets could be associated so that moving one sprocket also equally moved the other via hand-turned threaded bolts or any other sort of means. Still other means for adjusting could be effected by activation by the operator of a switch or lever; the switch or lever may, in turn, actuate fluid to be pumped into a cylinder or two cylinders which, in turn, caused the sprockets to move. However, whether simultaneous adjustment or alternate side adjustments were used to adjust the chains, or whether the adjustment was by hand or through the use of powered actuators, the operator first had to recognize that the load on the drag slats and the tension on the drag slats needed adjustment and then apply the adjustment.
What was needed was a system for monitoring and adjusting the tension on a drag slat chain to accommodate loads while minimizing wear on the chains. The system also needed to include a hard stop beyond which the chain could not be slackened in order to avoid having a chain jump the sprocket or other driving means. Further, the system would benefit from means to adjust the hard stop relative to the present state of wear or “slop” of the chain, and means to cause the motor to stop or stall to avoid damage.